We can tell he is because when Benvolio (his cousin suggests), he should see other woman and therefore
forget about or move on from Rosaline, his lover. Instead of doing so he says it will make him think about her
even more. This shows Romeo as a loyal lover because he just wants that girl and no one else.
In Benvolio's words: "By giving liberty unto thine eyes examine other
beauties!"
Passionate
His lover might not love him but he'll maybe try to convince them and do anything to
steal their heart, he'll eventually move on if he doesn't succeed but still is very
passionate about his love.
"Alas, that love, whose view is muffled still, Should, without eyes, see pathways to his will!" Love is
blind, but it can still make you do whatever it wants. This gives us an idea that he isn't responsible for
his actions love is.
Impulsive
We can see how quick he moves on with his lovers which may suggest that it wasn't
actually "true love" like he says. This shows us a clear picture of what kind of character
he is: he changes his mind often, he probably makes bad choices and is very gullible.
Peacefull
In my opinion he doesn't seem like a warrior/fighter he seems very calm. He might
dislike his parents for making bad decision (fighting) he blames everything on love and
doesn't hold any hatred for anyone
Emotionally unstable
Youthful/childish/immature
His emotions change very quickly and so do his actions, this shows us how sensitive he is due to taking a heart break so
seriously. Although he has true and powerful feelings, he can't take the fact that his lover can't and doesn't want to love him,
he doesn't want to respect her opinion which represents him as a young unintelligent character.
He is so depressed because his lover "won't be hit with Cupid's arrow."